Axial piston rotary apparatus

ABSTRACT

Axial piston pumps in which a series of pumping cells are mounted in a bent-axis holding structure, and in which each pumping cell has two cylinders and associated piston heads; the piston heads of each pumping cell are interconnected to one another so that liquid can flow from one cylinder to the other via the piston heads; liquid flow is controlled by means of one or more valve plates. The piston heads can be lengths of flexible tubing with the extremities closely fitting within axial bores in two facing barrels or, if it is desired to use only one valve plate, the lengths of tubing are bent in a U-shaped configuration and both extremities extend into the same barrel. In the latter case, the pumping cells can be duplicated but disposed in the opposite direction thus providing a twin pump.

United States Patent n91 Picker 51 Mar. 5, 197.4 Y

[54] AXIAL PISTON ROTARY APPARATUS 2,081,270 5/1937 Edmondson et a1. 91/500 [75] Inventor: Patrick Picker, Sherbrooke,

, Quebec Canada Primary ExammerWill1am L. Freeh Attorney, Agent, or Firm-Larson, Taylor and Hinds [73] Assignee: Universite de Sherbrooke,

Sherbrooke, Quebec, Canada [57] ABSTRACT I [22] Flled: May 1972 Axial piston pumps in which a series of pumping cells [21] A l, N 256,170 are mounted in a bent-axis holding structure, and in which each pumping cell has two cylinders and associated piston heads; the piston heads of each pumping [30] Fm-e'gn Apphcatlon 'Pnonty Data 9 cell are interconnected to one another so that liquid May 15, 1972 Canada 142187 can flow from one cylinder [0 the other via the piston heads; liquid flow is controlled by means of one or US. Cl. more valve plates [51] Int. Cl. F01b 13/04 The I piston heads can be lengths of flexible tubing with [58] Field of Search 91/500 417/427 504 the extremities closely fitting within axial bores in two UNITED STATES PATENTS 1,996,889 4/1935 Thomas 91/500 2,364,301 12/1944 MacNeil 91/500 2,813,493 11/1957 Aspelin v 91/500 2,914,219 11/1959 Chiantelassa. 91/500 3,434,429 3/1969 Goodwin 91/500 References Cited facing barrels or, if it is desired to use only one valve plate, the lengths of tubing are bent in a U-shaped configuration and both extremities extend into the same barrel. In the latter case, the pumping cells can be duplicated but disposed in the opposite direction thus providing a twin pump.

19 Claims, 11 Drawing Figures PATENIEIJHAR 51974 3795179 sum u [1F 4 1 AXIAL PISTON ROTARY APPARATUS This invention relates to hydraulic positive displacement rotary apparatus using axial pistons, and in particular to linearly variable displacement pumps.

Axial piston pumps are fairly well known in the art, and find numerous applications especially where a high-performance efficient pump having a high degree of controllability is called for. Such pumps however are normally designed for sustained high pressure operation, and due to their large number of closely fitting components, the cost factor has to a considerable extent limited their field of application.

The object of this invention is to provide a relatively simple axial piston pump which among other things can find application as a pulseless pump and affords highly linear variable displacement.

This invention therefore provides an axial piston pump wherein each pumping cell comprises two cylinders and a piston head for each cylinder, the piston heads in each pumping cell being interconnectedto one another, and valve means is provided which controls the flow of liquid in the cylinders whereby, during expansion of the cell, liquid enters at one of the cylinders and during compression is expelled at the other cylinder due to transfer of liquid from one piston to the other via said transfer means. The invention also provides an analytical, pump having either a single pumpin-g unit or two interrelated ones, together with control means for the. liquid flow rates.

In the accompanying drawings which illustrate examplar-y embodimentsof this invention,

'FIG. 1 is a cross-sectional view of a simple axial piston pump according to this invention;

FIG. 2. is a cross-sectional'view .of an axial piston pump in accordance with the invention using a single valve plate and U-shaped piston elements,

FIG. 3 is a plan view of a valve plate as can be used in the-pump shown in FIG. 2;

FIG. 4 is a simplified perspective view of a double unit pump with certain parts broken away for illustrative purposes;

FIG. 5 is an enlarged cross-sectional view of an analytical pump in accordance with this invention;

FIG. 6 is a plan view of a pair of twin pumps such as shown in FIG. 5 but mounted to a supporting structure for delivering two complementary liquid flow rates;

FIG. 7 is a view of one face of a guide member shown in FIG. 5 at-line A-A; I

FIG. 8 is aview of the other face of the guide member 'shown in FIG. 5 at line 8-8,

FIG. 9 is a view of one face of a barrel member shown in FIG. 5 at line C-C;

FIG. 10 is a view of the other face of the barrel member shown in FIG. 5 at line D-D;

FIG. 11, appearing on the sheet of FIGS. 1 to 4, is a graph illustrating the flow rate as a function of the angle of the bent axis for different speeds of rotation of the axial pumping cells.

With reference to the drawings, FIG. 1 illustrates a simple bent-axis axial piston rotary apparatus 10 wherein auxiliary components such as liquid seals have been omitted for clarity. Apparatus 10, to be considered as a pump for the purpose of the following description comprises two similar disc-shaped members 12, 13, with facing conical surfaces, spaced apart by a spherical spacer or'ball 14, and held to one another by external means (not shown) for universal motion. Member 13 has a cylindrical extension to permit members 12 and 13 to be driven into rotation in unison in a variable bent axis configuration. Members 12 and 13 also have series of circumferentially spaced axial bores or cylinders 16 to 19 into which project the opposite ends of tubular members 20, 21 forming piston heads. Tubular elements 20, 21 therefore span the space between the conical surfaces of members 12 and 13; since members 12 and 13 are intended to rotate in a bent-axis manner, means (not shown) would be required to prevent accidental withdrawal of the ends of tubular members 20, 21 from bores 16 to 19, such as a crown interconnecting the center points of all tubular members, or holding means for retaining one end of each tubular member to one of members 12 and 1-3.

Disc elements 24, with a kidney shaped port i.e. a semi-circular collector groove 26, 27 on their inner face can be used as valve means with provision for connection to output and input liquid ducts 28, 29. Preferably, valve-plates 24, 25 are mounted to a supporting structure (not shown), and are provided with a central bore for rotatably receiving therein extension 15 of member 12 and a similar extension 22 of member 13.

When driven into rotation, members 12 and 13 together with tubular members 20, 21 form ax'ial piston cells each comprising two piston means defined by the extremities of a tubular member 20, 21, two cylinder means defined by two associated axial bores 16 and 18 or 17 and 19 of members 12 and 13, and interconnecting duct means defined by the intermediate hollow region of a tubular member 20, 21.

Since for each complete revolution or cycle, the dis tance between two associated axial bores (16 and 18) or (17 and 19) gradually diminishes from top to bottom as seen in FIG. 1 and expands from bottom to top, every cell defined by a tubular member 20, 21 and a pair of associated axial bores (16 and18), (l7 and 19) effects a pumping action. Valve plates 24 and 25 are held stationary and are angularly positioned so that during the best part of the expansion half cycle of a pumping cell, its right-hand side cylinder 'means 18 or 19 as shown in FIG. 1 communicates with input duct 29 via the semi-circular collector 27 of valve plate 25 while the other cylinder means 16 or 17 is sealed by the inner face of valve plate 24. Conversely, during the most part of the compression half cycle of each pumping cell, the left-hand side cylinder means thereof (16 .or 17) registers with collector groove 26 of .valve plate 24 and hence communicates with outputduct 28 while the opposite cylinder means is sealed by the inner face of valve plate 25.

It will be seen that with a pumping apparatus as shown in FIG. 1, liquid emanating from duct 29 and rotor of the apparatus (12, 13, 20, 21) and/or'angle a of the bent-axis configuration. It was also found that due to the fact that liquid flow through the cells does not change direction, the response of a pump according to this principle but using a sufficiently large number of pumping cells isivirtually pulseless;-moreover, liquid' entrapment is minimum ple.

FIG. 2'shows in a manner similar to FIG. 1 a simple axial piston pump 30 wherein the tubular members 31 and washing is extremely sim- 3 and 32 are U-shaped, wherein all the axial bores 33, 34, 35, 36 are in the same conical member 40, the other member 41 merely holding and guiding the bases of the tubular member 31, 32, and wherein a double groove valve plate 44 controls the input and output flows across ducts 48 and 49. As in the case of the apparatus shown in FIG. 1, conical members 40, 41 and tubular members 31, 32 form a rotor whose components are held in a bent-axis configuration by means of an appropriate support structure (not shown).

Valve plate 44 is also shown in FIG. 3 which illustrates the inner face thereof. Semi-circular collector grooves 51 and 52 extend over circular arcs of approximately 175, are 180 apart and their respective radii of curvature correspond to the radial position of outer and inner axial bores 33, 36 and 34, 35 of conical member 40.

In operation therefore liquid flows from input duct 49 to inner groove 52 then into each pumping cell whose inner cylinder 34 or 35 registers with groove 52, gradually filling such pumping cell throughout the expansion half-cycle thereof. As the rotor continues its unidirectional angular motion, both cylinders 33 and 34 or 35 and 36 of a given expanded cell become sealed by the inner face of valve plate 44 since the angular extent of each groove 51 and 52 is less than 180. Beyond this short region, however, the outer cylinder 33 or 36 reaches groove 51 putting the associated pumping cell in communication with output duct 48 as compression of the cell begins.

It should be understood that in the arrangements shown in FIGS. 1 and 2, the number of pumping cells need not be restricted to two; the flow rate and the signal-to-noise ratio can in fact be increased by multiplying the number of such pumping cells.

In FIG. 4, an axial piston pump using U-shaped piston elements is illustrated in perspective view with certain elements partly broken for illustrative purposes. The principle of the pump of FIG. 4 is identical to that of FIG. 2. However, the components have been duplicated into a symetrical arrangement with respect to the central spherical spacer or ball 14, andthe conical members are made of two juxtaposed members. This provides two separate pumping circuits having like response characteristics.

The twin pump shown in FIG. 4 comprises starting from the left side of the drawing and proceeding to the right side of the drawing, a first double kidney ports valve plate 61 intended to remain stationary, a first disc-shaped barrel member 71, a first guide member 81, a spacer 14 in the form of a ball, a second guide member 82, a second disc-shaped barrel member 72,

and a second double groove valve plate 62 intended to be movable in a plane for varying angle 01" as desired. FIG. 4 shows two U-shaped piston elements 91 having their bases guided and retained by guide member 82 against barrel member 72, and the free ends of piston elements 91 extend through axial bores in guide member 81 and projectinto axial cylinder bores in barrel member 71. Also contemplated in the apparatus shown in FIG. 4 is a second series of U-shaped piston elements interleaved between piston elements 91 but extending in the opposite direction. This second series of piston elements is not shown in FIG. 4 but it should be under stood that their bases are guided and retained by guide member 81 against barrel member 71, and their free ends pass through axial bores (not shown) in guide member 82 and project into axial cylinder bores (not shown) in barrel member 72 in a manner similar to the first series of piston elements 91.

The outer faces of guide members 81, 82 are provided with an extension which extend through central apertures in their respective barrel members 7 1, 72 and valve plates 61, 62. It should be noted that the rotor of the twin pump shown in FIG. 4 comprises in addition to the above noted two sets of piston elements the guide members 81, 82, and the barrel members 71, 72 all of which being mounted and assembled to rotation in unison in a bent-axis configuration. The assembly provides two separate pumping units by reason of the fact that each valve plate 61 or 62 has two collector grooves separately communicating with inlet duct 101, 111 and outlet ducts 102, 112, and that liquid flowing into the inlet duct of one valve plate can flow through one series of piston elements and out through the same valve plate but cannot reach the other valve plate. It should also be realized that in the case of a symmetrical arrangement of identical components, the flow rates of the separate'pump units are identical since the speed of rotation w and the angle a are necessarily common to both units.

FIG- 5 is an enlarged longitudinal cross-sectional view of a twin analytical pump designed from the basic twin arrangement shown in FIG. 4. FIGS. 7, 8, 9 and 10 show faces of certain components of the pump of FIG. 5 as seen in the planes defined in FIG. 5 by arrows A-A, BB, CC, and D-D respectively. However, when comparing FIGS. 5 and 7, it will be seen that FIG. 5 has been purposely modified to show a representative one of the two sets of piston elements at 151, 152.

Pump is symmetrical with respect to spherical spacer 14 except for end fittings I22 and 123 and possibly screws 124 and 125. Therefore only one side of the pump need be described in detail. It will also be real ized that since this pump is of the axial piston type, the longitudinal axes of the two halves should be at an angle a for pumping to take place.

With reference to the left side portion of pump 120, a rotatable disc-shaped guide 131 is provided with its inner face 132 as shown in FIG. 8 and its outer face 133 according to FIG. 7. Guide 131' which may be fabricated of a suitably hard plastic material has an outwardly projecting extension 135 in the center of outer face 133. Two series of axial bores 136, 137 extend across faces 132, 133. These bores are equally spaced in two coaxial circular arrangements, and are disposed into generally radially aligned pairs. The purpose of these bores is to guide U-shaped piston elements 151, 152 to be described hereinafter. Hence the diameter of bores 136 and 137 should be slightly larger than the outside diameter of piston'elements 151, 152. Every alternate pair of bores 138 is designed to receive the base portion 153 of one of piston elements 151 and therefore a recess 139 is provided for-the piston 'element base to be received therein. The inner face 132 of-guide 131 as shown in FIGS. 5 and 8 comprises a socket 140 for centering guide 131 upon ball 14, and from socket 140 toward the periphery of guide 131, surface 132 is made slightly conical so as to allow opera tion of the pump in a bent-axis manner known per se. Bores 136 and 137 are countersunk as at 142 to reduce friction between guide 131 and piston elements 151,

Extension 135 is also provided with radial bores 161 for receiving the lower end of retaining pins 162 of which only one is shown in FIG. 5 but of which four are shown in FIG. 9, and toward the free end of extension 135, the diameter thereof is reduced so as to form an abutment 164 for the inner race 170 of thrust bearing 171. Guide 131 also has a longitudinally extending threaded bore 166. i

End fitting 122 which receives therein screw 124 has a reduced diameter portion 174 extending within inner race 170 of bearing 171 and an abutment 175 for supporting sprocket wheel 18 0 against spacer 181 and holding same against inner race 170. Sprocket wheel 180 may be used for driving a second pump, and the enlarged portion 176 of fitting 122 is intended to be coupled to a driving motor (not shown).

Extension 135 is designed to support disc-shaped barrel member 201 the inner face 202 thereof appearing in FIG. while FIG. 9 shows outer face 203. Barrel member 201 which may be fabricated of suitably inert plastic material for example that known under the trade mark Teflon contains a number of axial bores 210, 211 which form two series of cylinders for piston elements 152. Cylinders 210, 211 are adapted to align with alternate pairs of bores 136 and 137 of guide 131 between recesses 139 (see FIG. 7). Hence the total number of bores 210 and 211 of barrel member 201 is half that of guide 131. Inner face 202 of barrel member 201 is designed tovbear against outer face 133 of guide 131 and a recessed O-ring 220 around every bore 210, 211 is provided on inner face 202 of barrel 201 to seal the cylindersfrom guide 131. In order to retain barrel member 201 in a fixed position on extension 135, radial bores may be made through barrel member 201 to receive therein two or four retaining 'pins 162 which project into bores 161 in extension 135.

The outer face 203 of barrel member 201 being adjacent valve plate 250, suitable sealing must be accomplished to permit fluid flow between cylinders 210, 211 and the valve place collector grooves as noted before with reference to FIGS. 2 and 3 with minimum leakage and entrapment. In practice, three different sealing techniques have been used with success in the pump shown in FIG. 5 and indeed great caremust be exercised in this design area since barrel member 201 is intended to rotate relative to valve plate 250. Firstly, the adjacent surfaces of barrel member 201 and valve plate 250 should be machined with great precision, secondly,

they should be urged toward one another preferably by a pneumatic pressure as will be described hereinafter,

and unless the interface between barrel member 201 ,and valve plate 250 is flawless and remains so sufficiently long, an arrangement of resilient seals must be used.

A particularly long lasting sealing technique is shown in FIGS. 5 and9 where the outer face 203 of barrel member 201 carries three coaxial recessed O-rings 261, 262, 263 which seal cylinders 210 from the exterior and from cylinders 211 and which seal cylinders Pump 120 further comprises housing 270 having a recess 271 on inner surface 272 for at least partially receiving valve plate 250 therein. The outer surface 273 is provided with a first recess 274 for receiving the outer race of bearing 171 and a second recess 275 within the first one for clearing inner race 170.

The purpose of housing 270 is to permit clamping of pump section 130 onto a supporting structure as will be described hereinafter in connection with FIG. 6; but it also affords the provision of a small annular chamber 280 communicating with a source of low pressure gas shown at 281 serving as compressive means for applying pneumatic pressure axially inwardly against the outer surface of valve plate 250.

To this end gas sealing O-rings 283, 284 are recessed in the outer surface of valve plate 250 and O-ring 285 is similarly mounted to housing 270 around the central aperture thereof and on its inner recess surface 271.

Since valve plate 250 is intended to move slightly axially of housing 270, radial grooves 200 should be provided in housing 250 for longitudinal displacement of inlet and outlet ducts 48, 49. v g

Piston elements 151 and 152 can be used in varying numbers; for example, with reference to F IGS. 7 and 8, guide member 131 is designed to receive in alternate pairs 138 a total of eight piston elements oriented as at 151 and eight piston elements oriented as at 152 in the other alternate pairs. Piston elements 151 and 152 are of identical construction each consisting of'a length of flexible tubing made of a suitably inert plastic material for example Teflon. The plastic tubes are bent into a U-shape and the ends are successively threaded into a recessed pair of bores in one guide from the outer. surface thereof, then through a pair of plain bores of the other guide from the inner surface thereof and through O-rings 220 and a pair of bores 210, 211 of the barrel member adjacent the last named guide member.

In order to prevent withdrawal of the ends of piston elements 151, 152 from with the barrel members and also to keep the two guides against ball 14, suitable holding means such as tension springs seen only in FIG. 6 at 301 can be stretched across the two units of pump 120 and connected between the free ends of retaining pins 162 of barrel member 201 and the retaining pins (not shown) of the other barrel membenThese springs can also serveto relieve the piston elements 151, 152

of the shearing forces created by the frictional resistance to rotation of the slave pump unit (shown at 300 in FIG. 5) of pump 120 when the driving motor (not shown) rotates end-fitting 122 and the rotatable assembly of pump unit 130. To this end, retaining pins 162 of barrel member 201 lead those of the barrel member of pump unit 300 by a suitable angular difference so that during operation of pump the resistance to turning of pump unit 300 is compensated by the circumferential component of the combined spring tension forces.

The rotor of pump 120 therefore includes fitting 176, sprocket 180, spacer 181, the inner race of bearing 171 screw 124 and extension 135 with the associated guide member 131 and the adjacent barrel member 201, a similar assembly of components in pump unit 300 except for the lack of sprocket wheel and spacer, series of piston elements 151 and 152 and ball 14. The other components of pump unit are mounted to housing 270 which is designed to be fixedly supported, and

those of pump unit 300 although not rotating should be same speed.

ing a total of four liquid flows since each pump 320,

321 has two pumping units 331, 332, 333, 334. With this arrangement, the liquid flows of units 331 and 333 are complementary and so are those of units 332 and Supporting structure 330 comprises a base 341, a securing wall 342 through which extend the outer races of the ball bearings of pumping units 331 and 333 and an open wall 343 having elongated openings 344, 345 through which extend the outer races 348, 349 of the bearings of pumping units 332 and 334 in sliding engagement. Screws 350 are used to fixedly hold housings 351, 352 of pumping units 331, 333 to securing wall 342.

Motor 360 coupled to end fitting 361 of pumping unit 331 drives pumping unit 331 via coupling 363, and as indicated before, pumping unit 332 is also rotated, springs 301 relieving the piston elements 370 of excessive strain. Chain 375 interconnects end fittings 361 and 362 by means of two identical sprocket wheels 376 so that pump 321 is also driven into rotation at the In the central section 380 of open wall 343, a screw 381 is transversaly mounted in threading engagement with wall 343, and in the middle portion of screw 381, a small pulley 382 is secured for rotating the screw 381; a free space 383 in section 380 being provided for lateral displacement of pulley 382. The ends 391 and 392 of screw 381 are adapted to bear against bearings 348 and 349 so that upon rotation of screw 381 and translation thereof towards bearing 349, bearing 349 moves outwardly while bearing 348 due to the self centering effect of pump 320 follows end portion 391. In so doing, angle a of pump 320 decreases from its initial maximum value while that of pump 321 which at the outset is nil gradually increases so that when pump 320 reaches the straight line position, angle a of pump 321 becomes maximum.

In FIG. 6, a simple actuating mechanism 400 for rotating pulley 382 is illustrated; it consists ofa split tube 401 secured to wall 343 adjacent the central section 380 thereof, and an idler wheel 404' is rotatably mounted to the free end of tube 40] with its axis parallel to screw 381. A string entrained around pulley 382 and wheel 404 extends through slot 405 of tube 401 where it connects to a ring 406 as at 407 freely slidable along tube 40]; whereby upon displacement of ring 406 a given distance, for example one inch, angle a of pump 320 has decreased say one degree and that of pump 321 has increased also by one degree. The demultiplication factor of course will depend upon the size of pulley 382 and the pitch of screw 381. It should be understood, however, that no slipping should be allowed between the string andpulley 382. With this arrangement, it will be seen that a linear translator such as the X" ruler of an X-Y chart recorder can be used to move ring 406 to change the ratio of the fluid flows emanating from pumping units 331 and 333 and/or pumping units 332, 334 while directly recording on the chart the extent of a phenomenon relative to the ratio of the fluid flow rates.

Hence the pump system of FIG. 6 can find great applications where as in the field of dynamic microcalorimetry, two complementary pulseless pumps are sometimes required.

It will be noted that in FIG. 6, tubes 410 are used to supply low pressure air to pumping units 331 to 334 so as to create a pneumatic pressure as described hereinbefore in connection with FIG. 5. The inlet and outlet ducts, two for each pumping unit, have been omitted for simplicity as well as most retaining pins 411 and springs 301.

In practice, analytical pumps according to FIG. 5 have been used successfully using the sealing technique described above in connection with FIGS. 5 and 9. In an other embodiment, instead of recessed O-rings 261, 262, 263 and 270, a thin gasket of rubber (not shown) with apertures registering with cylinders 210, 211 has been found to give excellent results; in order to prevent angular displacement of the gasket between adjacent faces of the barrel member and the valve plate, the inner face of the gasket and the outer face 203 of the barrel member had been. depolished. The primary advantage of this sealing technique is the relative ease of manufacture of the thin inert rubber gasket, for example silicone rubber, which is significant since in the above described O-ring seal arrangement each O-ring must be inspected against microscopic imperfections. I have also found that good results are also obtainable if instead of using O-rings or a gasket the mating faces a the barrel member and valve plate are nearly mirror polished, no other seals are required provided the valve 'plate is made of a rigid but sufficiently yielding material and pneumatic pressure is applied behind the valve plate.

It should also be born in mind that the speed of rotation of analytical pumps as shown in FIGS. 5 and 6 should be relatively low, for example 10 rpm, and likewise, with piston elements having an inner diameter of 1/64 of an inch the flow rate of a pumping unit will be of the order of a few cubic centimeters per minute.

FIG 11 which represents the flow rate of a typical pumping unit as per FIG. 5 as a function of angle a for different speeds of rotation W,, W W shows the linearity of the relationship. In the structure of FIG. 6, it has been determined that the flow rates of two sideby-side pumping units are in fact virtually complementary; this can be theoretically shown assuming linear flow rates since for very small angles sine and tangent are equal.

I claim: 1

l. A hydraulic positive displacement rotary appara-v d. first valve means associated with said one cylindermeans, and permitting liquid inlet into said one cylinder means during the expansion period of the pumping cycle of said pumping cell, and preventing liquid expulsion out of said one cylinder means 3 during the compression period of said pumping cycle,

e. second valve means associated with said other cylinder means, and permitting liquid expulsion out of said other cylinder means during said compression period and preventing liquid inlet into said other Cylinder means during said expansion period,

f. pivot means adjustably coupling said piston means to form said pumping cells into a bent-axis configuration for universal motion of one piston means relative to the other,

g. and control means for varying the angle of the bent-axis configuration of said pumping cells;

said rotary apparatus also comprising actuating disc means adaptedto support said pumping cells, and while said apparatus is in operation, cause said piston means and cylinder means to effect a relative reciprocatory motion.

2. An axial piston pump comprising at least two pumping cells each comprising an elongated cylindrical hollow piston member made of flexible tubing of essentially constant cross-section defining at each extremity a piston head; said pump also comprising pivot means adjustably coupling two spaced apart disc members at different axial angular positions relative to each other, each disc member being provided with a series of axial bores conforming generally to the outside surface of i said piston head, said piston members extending between said disc members and having their piston heads engaged in said axial bores, whereby the axial bore associated with the first piston'head ofeach pumping cell defines a first cylinder and the bore associated with the I second piston head of each pumping cell defines a sec-,

ond cylinder; said pump further comprising first and second valve means respectively associated with the said first and second cylinders of each pumping cell, and inlet and discharge conduits respectively communicating with said first and second valve means, said first valve means permitting liquid transfer between said inlet conduit and the first cylinder of each said pumping cell during expansion thereof and isolating said first cylinders from said discharge conduit, and said second valve means permitting transfer of liquid between said discharge conduit and the second cylinder of each pumping cell during compression thereof and isolating said second cylinders from said inlet conduit, said pump also comprising control means for varying the relative angle between the two disc members, and drive means connectable with rotating 'motor means for rotation of said disc members and said piston members relative to said valve means.

3. An axial piston bent-axis analytical pump comprising first and second rotatable discshaped guide members adapted to be coupled to one another for universal motion, and-adapted to be driven into rotation in unison; a disc-shaped barrel member mounted for rotation with said first guide member, and on the axis of rotation thereof, and having its inner face disposed adjacent the outer face of said first guide member; said barrel member having at least two generally radially arranged pairs of axial bores defining cylinders; said pairs of cylinders being equally spaced apart from one another and from said axis of rotation; one U-shaped piston element for each one of said pairs of cylinders, each said piston element extending across the space between the inner faces of said guide members and being held in position by said guide members; each said piston element having its free ends defining a pair of piston heads interconnected to one another for liquid transfer from one each piston element being mounted for close sliding engagement within a corresponding one of said pairs of cylinders thereby defining a pumping cell; a stationary valve plate having on its inner face a kidney-shaped inlet port and a kidney-shaped outlet port; said ports having different radii of curvature extending from said axis of rotation and being angularly spaced apart from one another; the radius of curvature of said inlet port corresponding to the radial distance between one cylinder of each said pumping cell and said axis of rotation, and the radius of curvature of said outlet port corresponding to the radial distance between the other cylin der of each said pumping cell and said axisof rotation; the inner face of said valve plate closely conforming to the outer face of said barrel member; and inlet and outlet ducts respectively communicating with said inlet and outlet ports; whereby said valve plate controls liquid inlet to said one cylinder of each said cell and liquid outlet from said other cylinder of each said cell.

4. A pump defined in claim 3 wherein the centers of said inlet and outlet ports are angularly spaced from one another by l and wherein said'inl et and outlet ports are of equal angular extent less than I 5. A pump defined in claim 3 including compressive means adapted to maintain said first guide member, said barrel member and said valve plate against one another and permitting relative rotation of said barrel member and said valve plate.

6. A pump defined in claim 5 including a housing having a recess on the inner face thereof for receiving said valve plate and defining with the outer face of said valve plate a chamber, and low pressure gas feeding means communicating with said chamber for applying against said outer face of said valve plate an inwardly directed pneumatic pressure serving as compressive means. v

7. A pump as defined in claim 6 wherein said valve plate is made of plastic material with its inner face highly polished and wherein the outer face of said barrel member is highly polished.

8. A pump defined in claim 3 wherein each U-shaped piston element consists of a length of tubing made of flexible plastic material.

9. A pump defined in claim 3 including a spherical spacer between said first and second guide members, each said guide member having a hemispherical central socket for engagement with said spacer, said pump further comprising holding means for confining said spacer to said sockets.

10. A pump defined in claim 9 wherein said holding means comprises tension springs urging said guide members toward one another.

11. A pump defined in claim 9 wherein said first guide member includes a cylindrical extension project away from the outer face of said guide members; the

longitudinal axis of said extension coinciding with said I ring is provided around every cylinder.

13. A pump as defined in claim 12 wherein on the outer surface of said barrel member, a recessed O-ring is disposed around every cylinder, and three coaxially located recessed O-rings are disposed centrally of said pumps as defined in claim 12 and a supporting structure for holding the extension of the first guide member of each pump in a spaced apart parallel relationship, said structure including a translating device extending transversely of the axes of rotation of said extensions and adapted to displace the second guide members of said pumps in the same direction.

16. A pump defined in claim 11 wherein said second guide member is essentially identical to said first guide member, and additionally comprising a duplicate set of barrel member, valve plate, U-shaped piston elements and inlet and outlet ducts, said duplicate barrel mem- 12 ber and valve plate being mounted to the extension of said second guide member, and said duplicate U- shaped piston elements extending across the space between the inner faces of said guide members, with their piston heads closely fitting within cylinders in said duplicate barrel member thereby forming a duplicate set of pumping cells.

17. A pump defined in claim 16 wherein each guide member incorporates a number of radial pairs of axial bores equal to the total number of said pumping cells and duplicate pumping cells, for the purpose of slidingly guiding the intermediate portions of every piston element and duplicate piston element.

18. A pump defined in claim 17 wherein recesses are provided on the outer face of said first guide member for receiving the base portions of said duplicate piston I elements, and wherein corresponding recesses on the dial bore in said guide members is countersunk on the inner faces of said guide members, and wherein said guide member inner faces are slightly conical. 

1. A hydraulic positive displacement rotary apparatus comprising at least two pumping cells each comprising: a. two piston means, b. b. two cylinder means each receiving therein a corresponding one of said piston means, c. duct means interconnecting said piston means for allowing liquid flow from one of said cylinder means to the other one of said cylinder means, d. first valve means associated with said one cylinder means, and permitting liquid inlet into said one cylinder means during the expansion period of the pumping cycle of said pumping cell, and preventing liquid expulsion out of said one cylinder means during the compression period of said pumping cycle, e. second valve means associated with said other cylinder means, and permitting liquid expulsion out of said other cylinder means during said compression period and preventing liquid inlet into said other cylinder means during said expansion period, f. pivot means adjustably coupling said piston means to form said pumping cells into a bent-axis configuration for universal motion of one piston means relative to the other, g. and control means for varying the angle of the bent-axis configuration of said pumping cells; said rotary apparatus also comprising actuating disc means adapted to support said pumping cells, and while said apparatus is in operation, cause said piston means and cylinder means to effect a relative reciprocatory motion.
 2. An axial piston pump comprising at least two pumping cells each comprising an elongated cylindrical hollow piston member made of flexible tubing of essentially constant cross-section defining at each extremity a piston head; said pump also comprising pivot means adjustably coupling two spaced apart disc members at different axial angular positions relative to each other, each disc member being provided with a series of axial bores conforming generally to the outside surface of said piston head, said piston members extending between said disc members and having their piston heads engaged in said axial bores, whereby the axial bore associated with the first piston head of each pumping cell defines a first cylinder and the bore associated with the second piston head of each pumping cell defines a second cylinder; said pump further comprising first and second valve means respectively associated with the said first and second cylinders of each pumping cell, and inlet and discharge conduits respectively communicating with said first and second valve means, said first valve means permitting liquid transfer between said inlet conduit and the first cylinder of each said pumping cell during expansion thereof and isolating said first cylinders from said discharge conduit, and said second valve means permitting transfer of liquid between said discharge conduit and the second cylinder of each pumping cell during compression thereof and isolating said second cylinders from said inlet conduit, said pump also comprising control means for varying the relative angle between the two disc members, and drive means connectable with rotating motor means for rotation of said disc members and said piston members relative to said valve means.
 3. An axial piston bent-axis analytical pump comprising first and second rotatable disc-shaped guide members adapted to be coupled to one another for universal motion, and adapted to be driven into rotation in unison; a disc-shaped barrel member mounted for rotation with said first guide member, and on the axis of rotation thereof, and having its inner face disposed adjacent the outer face of said first guide member; said barrel member having at least two generally radially arranged pairs of axial bores defining cylinders; said pairs of cylinders being equally spaced apart from one anoTher and from said axis of rotation; one U-shaped piston element for each one of said pairs of cylinders, each said piston element extending across the space between the inner faces of said guide members and being held in position by said guide members; each said piston element having its free ends defining a pair of piston heads interconnected to one another for liquid transfer from one said piston head to the other; both said piston heads of each piston element being mounted for close sliding engagement within a corresponding one of said pairs of cylinders thereby defining a pumping cell; a stationary valve plate having on its inner face a kidney-shaped inlet port and a kidney-shaped outlet port; said ports having different radii of curvature extending from said axis of rotation and being angularly spaced apart from one another; the radius of curvature of said inlet port corresponding to the radial distance between one cylinder of each said pumping cell and said axis of rotation, and the radius of curvature of said outlet port corresponding to the radial distance between the other cylinder of each said pumping cell and said axis of rotation; the inner face of said valve plate closely conforming to the outer face of said barrel member; and inlet and outlet ducts respectively communicating with said inlet and outlet ports; whereby said valve plate controls liquid inlet to said one cylinder of each said cell and liquid outlet from said other cylinder of each said cell.
 4. A pump defined in claim 3 wherein the centers of said inlet and outlet ports are angularly spaced from one another by 180* and wherein said inlet and outlet ports are of equal angular extent less than 180*.
 5. A pump defined in claim 3 including compressive means adapted to maintain said first guide member, said barrel member and said valve plate against one another and permitting relative rotation of said barrel member and said valve plate.
 6. A pump defined in claim 5 including a housing having a recess on the inner face thereof for receiving said valve plate and defining with the outer face of said valve plate a chamber, and low pressure gas feeding means communicating with said chamber for applying against said outer face of said valve plate an inwardly directed pneumatic pressure serving as compressive means.
 7. A pump as defined in claim 6 wherein said valve plate is made of plastic material with its inner face highly polished and wherein the outer face of said barrel member is highly polished.
 8. A pump defined in claim 3 wherein each U-shaped piston element consists of a length of tubing made of flexible plastic material.
 9. A pump defined in claim 3 including a spherical spacer between said first and second guide members, each said guide member having a hemispherical central socket for engagement with said spacer, said pump further comprising holding means for confining said spacer to said sockets.
 10. A pump defined in claim 9 wherein said holding means comprises tension springs urging said guide members toward one another.
 11. A pump defined in claim 9 wherein said first guide member includes a cylindrical extension project away from the outer face of said guide members; the longitudinal axis of said extension coinciding with said axis of rotation, said extension supporting said barrel member for rotation therewith and rotatably mounting said valve plate.
 12. A pump as defined in claim 11 wherein on the inner face of said barrel member, a recessed sealing O-ring is provided around every cylinder.
 13. A pump as defined in claim 12 wherein on the outer surface of said barrel member, a recessed O-ring is disposed around every cylinder, and three coaxially located recessed O-rings are disposed centrally of said barrel member; said coaxially located O-rings being respectively located around between and within said cylinders.
 14. A pump as defined in claim 12 wherein an apertured disc-shaped silicone rubber gasket is disposed between tHe inner face of said valve plate and the outer face of said barrel member, the inner face of said gasket and the outer face of said barrel member being depolished while the outer face of said gasket and the inner face of said valve plate are relatively well polished.
 15. A pump assembly comprising two axial piston pumps as defined in claim 12 and a supporting structure for holding the extension of the first guide member of each pump in a spaced apart parallel relationship, said structure including a translating device extending transversely of the axes of rotation of said extensions and adapted to displace the second guide members of said pumps in the same direction.
 16. A pump defined in claim 11 wherein said second guide member is essentially identical to said first guide member, and additionally comprising a duplicate set of barrel member, valve plate, U-shaped piston elements and inlet and outlet ducts, said duplicate barrel member and valve plate being mounted to the extension of said second guide member, and said duplicate U-shaped piston elements extending across the space between the inner faces of said guide members, with their piston heads closely fitting within cylinders in said duplicate barrel member thereby forming a duplicate set of pumping cells.
 17. A pump defined in claim 16 wherein each guide member incorporates a number of radial pairs of axial bores equal to the total number of said pumping cells and duplicate pumping cells, for the purpose of slidingly guiding the intermediate portions of every piston element and duplicate piston element.
 18. A pump defined in claim 17 wherein recesses are provided on the outer face of said first guide member for receiving the base portions of said duplicate piston elements, and wherein corresponding recesses on the outer face of said second guide member receive the base portions of said piston elements.
 19. A pump as defined in claim 18 wherein every radial bore in said guide members is countersunk on the inner faces of said guide members, and wherein said guide member inner faces are slightly conical. 